Detecting respiration of a patient is desirable, for example to detect abnormal respiration indicating that the patient is in need of attention. There are many existing techniques to detect respiration, such as impedance plethysmography (the standard for hospital monitoring), strain gauges around the patient's chest and/or abdomen, magnetometers, a Respitrace Impedance Plethysmograph (a band around the chest and abdomen), pressure-sensing mattresses, mattresses that sense movement through capacitive sensors, and direct measures of airway flow, either with a mask or through attachment to an artificial airway of a patient. All of these techniques employ physical contact of one or more apparatus with the patient.
Several techniques exist to monitor vital signs of a patient without direct physical contact with the patient. For example, microwave radar may be used with antennas disposed above a prone patient, e.g., attached to a ceiling above a bed on which the patient lies. Other examples include thermal infrared (with the patient's face being uncovered and kept in view of a thermal-sensing camera), and direct video inspection (with the patient being uncovered or covered but with markings placed on the patient). Laser interferometry may also be used to monitor patient respiration if radio interference, interference with materials covering the patient, and laser aiming issues are addressed.